fixed broken streams.spec.js testcases which used outdated API
* removed all sender references from testcases
* updated tests to use the stream/encoder API
* dropped the use of a mockSender and use the debugStreamFactory instead
Changed timestamps to use literal int64 values instead of taking in a JS Date object
* more test cleanups to use new API
* updated timestamp verification to use Long.js as we need to support
  int64 values as hekad expects nanosecond timestamps
* added tests around the FileStream